Issue |
A&A
Volume 412, Number 1, December II 2003
|
|
---|---|---|
Page(s) | 175 - 184 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20031417 | |
Published online | 25 November 2003 |
A massive disk/envelope in shocked H2 emission around an UCHII region
1
Centro de Astrofísica da Universidade do Porto, Rua das Estrelas, 7150-462 Porto, Portugal
2
Instituto Superior da Maia, Av. Carlos Oliveira Campos, 4475-690 Avioso S.Pedro, Portugal
3
Harvard Smithsonian Center for Astrophysics, 60 Garden Street, MS-78 Cambridge, MA 02138, USA
4
Joint Astronomy Center, 660 N. A'ohōkū Place, University Park, Hilo, HI 96720, USA
5
Instituto de Astronomia, UNAM-Morelia, Apartado postal 3-72, CP 58090 Morelia, Michoacan, Mexico
Corresponding author: M. S. N. Kumar, nanda@astro.up.pt
Received:
23
April
2003
Accepted:
2
September
2003
A multi-wavelength study of IRAS 07427–2400 in line and
continuum emission was conducted to investigate the nature of a H2
–0 S(1) line emitting feature around this ultra-compact HII
region. High resolution 3.6 cm continuum observations from the Very
Large Array and 350 μm continuum observations from the Caltech
Submillimeter Observatory, combined with archival far-infrared data of
IRAS 07427–2400 show a flux density distribution indicating a
luminous (
) point source associated
with an ultra-compact HII region. A Grey body model fit to the flux
density distribution yields a dust emissivity index
(
) indicative of a circumstellar disk/envelope. Our
C18O map shows a dense core centered on the continuum source,
with the major axis roughly aligned with the H2 feature. A
position-velocity diagram of the C18O core obtained along the
major axis shows rotation with a velocity gradient of
~0.1 km s-1 arcsec-1. New CO
–2 maps of the
region are presented which reveal a massive molecular outflow from the
IRAS source. We argue that the H2 feature arises in a
disk/envelope around IRAS 07427–2400 and not in an outflow. We
present a near-infrared HK band spectrum of the H2 features that
shows several ro-vibrational emission lines of H2 and [FeII].
Analysis of the line ratios indicates that the line emission is
shock-excited and not due to fluorescence. We estimate an excitation
temperature of ~1600 K and an average extinction of
mag to the H2 feature. The line fluxes yield a mass
accretion rate of
yr-1 and a lifetime of
~5360
1200 yr resulting in a disk/envelope mass of
140
50
. The resulting Jeans Mass of 2420
indicates that the disk/envelope will not undergo fragmentation.
IRAS 07427–2400 represents one of the most massive YSOs known to date
forming by means of accretion.
Key words: stars: formation / accretion: accretion disks / interstellar medium: jets and outflows / ISM: HII regions
© ESO, 2003
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